Chop potatoes into 1” cubes, slice onion into 1/2” rounds, slice mushrooms in half, place all in a large mixing bowl, add the whole tomatoes, olive oil and sherry vinegar and mix thoroughly to coat all vegetables. Add 1 1/2 teaspoon kosher salt and a large pinch of black pepper and mix to coat. Scoop the vegetable mixture from the bowl and lay on a sheet pan lined with parchment. Place chicken hindquarters in the bowl with residual seasoning and mix to coat on all sides, add an additional teaspoon of salt to fully coat the chicken. Place the chicken hindquarters on the sheet pan, moving aside the vegetable mix to create space as needed. Bake for 50 minutes. Remove from oven, let cool for 30 minutes, sprinkle with parsley leaves.